Rename stereo video codec to multiplex

This CL only does the rename from"stereo" to multiplex". With this we have a
better name that doesn't clash with audio's usage of stereo.

Bug: webrtc:7671
Change-Id: Iebc3fc20839025f1bc8bcf0e16141bf9744ef652
Reviewed-on: https://webrtc-review.googlesource.com/43242
Commit-Queue: Emircan Uysaler <emircan@webrtc.org>
Reviewed-by: Niklas Enbom <niklas.enbom@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21769}
diff --git a/modules/video_coding/video_codec_initializer.cc b/modules/video_coding/video_codec_initializer.cc
index 24c9e7c..8a86571 100644
--- a/modules/video_coding/video_codec_initializer.cc
+++ b/modules/video_coding/video_codec_initializer.cc
@@ -39,7 +39,7 @@
     bool nack_enabled,
     VideoCodec* codec,
     std::unique_ptr<VideoBitrateAllocator>* bitrate_allocator) {
-  if (PayloadStringToCodecType(settings.payload_name) == kVideoCodecStereo) {
+  if (PayloadStringToCodecType(settings.payload_name) == kVideoCodecMultiplex) {
     VideoSendStream::Config::EncoderSettings associated_codec_settings =
         settings;
     associated_codec_settings.payload_name =
@@ -49,7 +49,7 @@
       RTC_LOG(LS_ERROR) << "Failed to create stereo encoder configuration.";
       return false;
     }
-    codec->codecType = kVideoCodecStereo;
+    codec->codecType = kVideoCodecMultiplex;
     strncpy(codec->plName, settings.payload_name.c_str(),
             sizeof(codec->plName));
     return true;